This error is directly connected to keys, and old widevinecdm.dll. Google has revoked old widevinecdm.dll keys, so new keys for newer widevinecdm.dll are needed.
But weren't the older cdm versions disabled around September 5th?
I was still able to use old cdm version on September 5th, it only stopped working (on all sites) on September 6th.
You were having key problems before September 5th.